564 SIGHT. 



the lachrymal sac, and thence pass into the lower meatus of the 

 nostrils." x 



The tears appear to me to pass over the ball of the eye as 

 low as the edge of the superior tarsus, which is so applied to the 

 ball as not ordinarily to allow of their ready escape under it. y As 

 the upper lid descends and nearly covers the front of the eye 

 during sleep, for the lower has but little motion and the fine inner 

 edges of both meet, the whole of the ball is at this time readily 

 preserved moist. But, when the eyes are open, the front of the 

 eye between the lids would not be moistened unless the upper 

 tarsus occasionally descended with the fluid contained behind it. 

 A portion of the fluid, thus brought down upon the front of the 

 eye, remains after the upper lid rises again after winking, and 

 trickles by its gravity as far as the inferior tarsus, which, ascend- 

 ing a little as often as the superior descends, raises it somewhat. 

 Winking thus preserves the front of the eye constantly moist 

 during the waking state. The under eyelid in rising moves to- 

 wards the nose, as Sir C. Bell pointed out, and thus directs the 

 tears towards the puncta, and extraneous matters are both pushed 

 and washed towards the inner canthus, where the tears are always 

 seen to run over first. 



It may be also observed that, when the tarsi approximate, as 

 they drive before them the moisture of the front of the eye-ball, 

 and the lower at the same time moves it somewhat towards the nose, 

 they quite inundate the puncta lachrymalia, by which circumstance 

 the puncta are, of course, enabled to carry off a large quantity of 

 the secretion, and ordinarily to prevent its overflow, which would 

 occur at the centre of the lower tarsus. During sleep the puncta 

 are not so copiously supplied, as they have only the same share 

 of tears as the eye in general ; and there is less occasion for it, 

 because the removal of the stimulus of air and light by the closure 

 of the eyelids lessens the secretion. 



* " J. Chr. Rosenmiiller, Organor. lachrymalium partiumque externarum 

 oculi humani Descriptio Anatomica. Lips. 1797. 4to. 



y The object of this firm application of the tarsi to the eye must be the exclu- 

 sion of foreign matters from the orbit. Sir C. Bell says that the margins of the 

 eyelids touch at their outer edges only, and leave a gutter between them and the 

 cornea. I cannot conceive this, as the inner edge of the tarsi appears firmly 

 applied to the eye. PhiL Trans. 1823. 



